Q: An auto reply set up in mail does not now operate

Hi Designmap,
 

Thanks for contributing to the Apple Support Communities. 
 

It looks like Mail isn't following your Mail rule to reply to messages that meet certain criteria. 
 

Before troubleshooting, be sure to update to the latest version of OS X (currently 10.11.1)--How to get software updates for your Mac.
 

If your reply rule still isn't working, try deleting and recreating it. 
 

For reference, here are the steps to create a reply rule from Mail (El Capitan): Reply to, forward, or redirect messages:
 

Automatically reply to or forward messages

Mail must be open before it can automatically forward or reply to messages. If you want to send automatic replies when Mail isn’t open—like when you’re on vacation—check with the provider of your email account. 

1. Choose Mail > Preferences, then click Rules.

2. Click Add Rule, then type a name for the rule.

3. Indicate whether any or all of the conditions must be true for the rule to be applied.

4. Set the conditions that determine which messages to automatically reply to or forward.

5. Choose options from the “Perform the following actions” pop-up menu.

    
    
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     Forward messages: Choose Forward Message from the first pop-up menu, then enter the email addresses where you want to receive the forwarded messages. Click Message, then enter any text you want to include with the forwarded message. For example, you could explain that you’re automatically forwarding messages. 

      
    
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     Reply to messages: Choose “Reply to Message” from the first pop-up menu, click “Reply message text,” then enter your reply. Mail includes the full text of the original message in your reply. 

      

6. Click OK.

Carefully consider the rules you create. If they’re too broad, messages can be sent inadvertently or create loops (replies to replies you sent). If possible, test the rules.

Safe Computing.